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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.unix.wizards
Subject: Re: DEC DELUA or Interlan N1010A ??
Message-ID: <7873@utzoo.UUCP>
Date: Sat, 4-Apr-87 20:50:25 EST
Article-I.D.: utzoo.7873
Posted: Sat Apr  4 20:50:25 1987
Date-Received: Sat, 4-Apr-87 20:50:25 EST
References: <552@hsi.UUCP>
Organization: U of Toronto Zoology
Lines: 25

> Given the choice of a DEC DELUA or a Micom/Interlan N1010A for a
> VAX 8600, which Ethernet interface would you choose ?  ...

I don't know anything about the DELUA, but it may well have considerably
higher performance than the 1010A.  [Brief digression:  I assume that a
N1010A is the same interface I know as an NI1010A.]  I ran an experiment
on the 1010A which produced some very unimpressive numbers for its
transmit performance.  I coded a little standalone code loop that just
threw the same packet into the interface over and over, and then timed
the result on the cable.  (I had an oscilloscope watching the cable for
other reasons.)  The machine was an 11/44, i.e. slightly faster than a
750, so I doubt that the CPU was a big bottleneck.  I plotted packet
frequency versus packet length, and got a nice straight line.  Sending
an N-byte packet via the NI1010A takes 600 + 3.3N microseconds.  Note
that the time on the cable itself is about 20 + 0.8N, so this is *not*
very impressive throughput.

I have no specific idea where the 600-us overhead comes from.  The extra
time per byte is probably at least partly, I'd guess, inefficient Unibus
DMA.  Smarter DMA and a multi-packet transmit buffer (so that one could be
DMAing in from the Unibus while another was being transmitted) could improve
things a lot, I suspect.
-- 
"We must choose: the stars or	Henry Spencer @ U of Toronto Zoology
the dust.  Which shall it be?"	{allegra,ihnp4,decvax,pyramid}!utzoo!henry